1. Field of the Invention
The present invention relates to a power supply apparatus and an image forming apparatus, and more particularly, to an insulated DC-to-DC converter for obtaining power under a state in which direct current voltages each obtained by rectifying and smoothening an alternating voltage are insulated from each other, as a switching DC-to-DC converter that achieves such insulation through capacitors.
2. Description of the Related Art
In an insulated DC-to-DC converter for transmitting power while insulation is secured between a primary circuit electrically connected to an alternate current power supply and a secondary circuit directly connected to a user accessible portion, a transformer is used in general. On the other hand, for example, in Japanese Patent Application Laid-Open No. H02-081212, there is proposed a power conversion system using not a transformer that once converts electrical energy into magnetic energy but capacitors that convert electrical energy into electric field energy to secure insulation.
However, in Japanese Patent Application Laid-Open No. H02-081212, one output terminal is connected to a grounding point (hereinafter referred to as GND). Therefore, with regard to the capacitors that perform the insulation and power supply, only a part of a current that flows from one of the capacitors flows into another of the capacitors, and the two capacitors lack in balance. As a result, the rest of the current that flows from the one capacitor flows out of the apparatus via GND, and thus, various measures are necessary against electro-magnetic interference (EMI), in particular, a noise terminal voltage.